What email client for the Mac is bug-free and works as advertised?

I have a couple of clients who need to be able to access a LARGE database of mail going back a few years. On their Windows machines, using Outlook PST files, that was easy if a bit slow: create separate “personal folders” files, drag and drop. Compact the files afterwards. Simple, effective, no issues.

Entourage for Mac (Office 2008): database crashes and corrupts all the data. Outlook for Mac (Office 2011): same again. Thunderbird: hangs, sends the most unbelievable ransom-note formatted mails. Mac Mail: can’t handle embedded graphics.

Someone must have a solution to this. Everyone is using email as a filing system nowadays, I cannot believe that my problem is unique. Anyone able to help?

Chris